1. Field of the Invention
The present invention relates to a high radiation concentration photovoltaic cell system, and more particularly to an optical structure, constituting light radiation concentrators for photovoltaic cells in combination with a solar radiation collecting and/or reflecting device, forming a photovoltaic cell system.
2. Discussion of Background
Solar photovoltaic cells are usually produced as small units, each capable of producing limited electric power in the range of a few watts. For large scale applications, it is necessary to integrate many cells to form a module that can produce higher electric power. Due to mechanical limitations, very close packing of cells is very difficult and in many cases, each cell has a small area with inactive material. When such a module is formed, a portion of the area of the module is inactive and when oriented towards the sun, a fraction of the light that is incident on this area is not utilized. Moreover, when the module is used for converting concentrated solar radiation to electricity, this fraction of concentrated radiation can damage the module.
In cases where a powerful solar radiation source is used, a multitude of solar cells are necessary for the conversion of all available solar radiation light to electric power. A homogenous or stable distribution of light is important for designing parallelly or serially connected cells, since the output of single module does not provide sufficient current or voltage large scale systems.
Using non-ideal radiation collecting systems, however, the concentrated solar light at the focal point is not homogeneous and usually it is more concentrated at the center of the radiated beam. The distribution of light within the beam varies with time due to astigmatism and other aberrations of the concentrating devices. Moreover, when selective spectrum illumination is used to excite the cells, very high initial concentration is required. As an example, it can be shown that commercial cells are available that operate efficiently at solar concentrations of 500 suns with efficiency more than 20%. Experiments carried out demonstrated that if only the spectral band between 0.7 and 0.9 micron is used, the efficiency increases to 43%. This spectral band contains only 20% of the incident solar radiation and hence, in order to achieve the same concentration, a concentration factor of 2500 is needed. In order to achieve this concentration, solar radiation tracking systems are necessary when utilizing a dish-like system, a concentration factor of 10000 can be achieved, but in central receiver systems a non-imaging concentrator is needed.